T Lymphocytes

Question 1

Describe the structure of a TCR

Answer 1

Alpha and beta chain but some have beta and gamma
Fab and Fc regions
Part of the immunoglobulin family
Chains are not very long but are natively charged so interact with +ve charges in T

Question 2

When antigen binds to TCR?

Answer 2

CD3 has long cytoplasmic tail
Phosphorylation of tyrosine when antigen binds
Triggers chemical cascade

Question 3

How are the alpha and beta chains rearranged?

Answer 3

Beta is rearranged first VDJ

Alpha arranged next VJ

Question 4

TCR checkpoint

Answer 4

If the TCR doesn’t recognise MHC= useless

If it binds to MHC even when there is no antigen = dangerous

Question 5

Maturing T in the thymus

Answer 5

In the cortex, T cells express CD4, CD8 and preTCR
The preTCR then becomes TCR
Either CD4 or CD8 is expressed

Question 6

T cell classes

Answer 6

Cytotoxic T = CD8 binds to MHC class I = kill
Helper T1 = CD4 binds to MHC class II = inflammatory response
Helper T2= CD4 binds to MHC class II = activate B

Question 7

Structure of MHC class I

Answer 7

Alpha chain is heavy and variable
Beta microglobulin is light and the same in everyone 
NON COVALENTLY linked
Part of the immunoglobulin family 
Alpha 1,2,3 beta

Question 8

Structure of MHC class II

Answer 8

Same as class I
BUT 2 polypeptides equal in size and both transmembranal
Alpha 1, beta 1, beta 2, alpha 2

Question 9

MHC class I and II present which kinds of peptide?

Answer 9

Class I = 8-10 amino acids long

Class II = 13+ sticks out

Question 10

How does a peptide bind to MHC

Answer 10

Parts of the peptide that are the same bind to binding pockets

Question 11

What is HLA?

Answer 11

Humans leukocyte antigen = human MHC 
Three types of class I =A,B,C
Three types of class II =DP, DQ, DR

Question 12

Why do we have different responses to the same disease?

Answer 12

We have variation in the alleles that code for MHC

Question 13

Endogenous and exogenous antigens?

Answer 13

Endogenous are inside a cell e.g. virus , presented by MHC class I for cytotoxic t 
Exogenous= outside the cell e.g. phagocytosis, presented by class II to helper T

Question 14

Endogenous

Answer 14

Viral proteins in cytoplasm
Processed by proteasome
Peptide moves into ER by TAP (transport associated with antigen processing)
MHC synthesised in ER and binds to chaperone protein
Go to Golgi and presented in surface

Question 15

Exogenous

Answer 15

Protein taken into cell
Processed in endocytic vesicles
Class II enters ER
Binds to invariant chain so MHC doesn’t bind to a peptide
Invariant cain digested
= MHC and CLIP (class II associated invariant chain peptide)
Swap CLIP for antigen 
Move to surface